Linux basics and documentation

• Linux is a Unix-like operating system that is free to use and freely disseminated
• It has a very wide range of applications in the server-side field and embedded field.

2. Version

Divided into kernel version and hairstyle version

• kernel
• Each manufacturer will make its own distribution version
  • redhat
  • CentOS
  • ubuntu
  • fedora

3. The difference between Linux and Windows

• Linux is strictly case sensitive
• All content in Linux is saved in the form of files, including hardware, users and files.
• Linux does not distinguish file types by extensions, but by permissions. However, there are some agreed extensions for administrators to see.
  • Compressed package .gz .bz2 .tar.bz2 .tgz
  • binary file .rpm
  • Web page file .html .php
  • Script file .sh
  • Configuration file .conf
• Programs under Windows cannot be installed and run directly in Linux
• Linux uses more character interfaces
  • Occupies less system resources
  • Reduces the possibility of errors and attacks, making the system more stable

How to buy a server

• Alibaba Cloud ECS
• Amazon AWS
• Baidu Cloud

4. Connect to server

• git bash
• mac shell
• xshell4
• xftp4

5. Partition

Disk partitioning is dividing the disk into several logical parts using a partition editor
Once the disk is divided into multiple partitions, different types of directories and files can be stored in different partitions.

6. mount point

• In order to make these partitions accessible in the Linux system, these partitions need to be mounted to the corresponding directories.
• In Linux, the directory is called a mount point.
• The process of linking directories and partitions together is called mounting
• / is the root directory and must be mounted on a partition. By default, all subdirectories will be written to this partition.
• All subdirectories under the same level directory can have their own independent storage space
• Required partitions
  • /root partition
  • Swap partition (swap partition, virtual memory, generally 2 times the memory, not more than 2G)
• Recommended partition
  • /boot (boot partition, 200M) separate partition to avoid the system being unable to start due to the partition being full.

linux common commands

1. Directory

Contents	Purpose
/	root directory
/boot	Start directory, start related files
/dev	device file
/etc	configuration file
/home	The home directory of ordinary users, which can be operated
/lib	System library storage directory
/mnt	Mobile device mounting directory
/media	CD mounting directory
/misc	Tape drive mounting directory
/root	The home directory of the super user, which can be operated
/tmp	Temporary directory, operable
/proc	Running kernel information mapping, mainly outputs process information, memory resource information, disk partition information, etc.
/sys	Driver information for hardware devices
/var	variable
/bin	Common basic commands, such as ls, chmod, etc., can also be used by ordinary users
/sbin	Basic system commands, such as shutdown and reboot, are used to start the system and repair the system. Only administrators can run it
/usr/bin	is the running script for some software you install later
/usr/sbin	Place some necessary programs for system management installed by users

1.2 Basic command format

1.2.1 Command prompt

[root@localhost ~]#

• root currently logged in user
• localhost host name
• ~ The current working directory, the default is the current user's home directory, root is /root, ordinary users are /home/username
• Prompt: Super user is #, ordinary user is $

1.2.2 Command format

• command [options] [parameters]
• When there are multiple options, they can be written together
• General parameters can be written in two ways: simplified and complete. -a is equivalent to --all

1.2.3 ls

• Query the contents of the directory
• ls [options] [file or directory]
• Options
  • -a displays all files, including hidden files
  • -l show detailed information
  • -d View the properties of the directory itself rather than the subfiles ls /etc/
  • -h displays file size in a user-friendly manner
  • -i displays inode, which is the i node. Each node has an ID number.
• Default file list in the current directory

1.2.3.1 -l

Show details

drwxr-xr-x .  1 root  root   800 Sep 16 00:19 logs

drwxr-xr-x	.	1	root	root	800	Sep 16 00:19	logs
File Types and Permissions	ACL Permissions	Hard Link Reference Count	Owner	Group	File Size	Last Modified	File Name

1.2.3.2 File types and permissions

-rw-r--r--

• File type - file, d directory, l soft link file
• u(owner), g(group), o(others)
• r(read) reads, w(write) writes, x(execute) executes

1.3 File processing commands

1.3.1 mkdir

• Make directory make directory
• mkdir -p [directory name]
  • -p create recursively

1.3.2 cd

• Change directory change directory
• cd [directory]
  • ~ Home Directory
  • home directory
  • last directory
  • . current directory
  • .. Parent directory
• Relative paths refer to the current directory
• The absolute path starts from the root directory
• Press TAB to complete commands and directories

1.3.3 pwd

• show current directory pwd

1.3.4 rmdir

• remove directory remove empty directory
• rmdir [directory name]

1.3.5 rm

• Delete a file or directory remove
• rm [file or directory]
  • -r delete directory
  • -f force deletion
• rm -rf file or directory] Forcefully delete all directories recursively

1.3.6 cp

• copy copy command
• copy [source file or directory] [destination file]
  • -r copies directories, the default is to copy files
  • -p copy with file attributes
  • -d If the source file is a linked file, copy the connection attributes
  • -a is equivalent to -rpd

1.3.7 mv

• Move a file or rename it move
• mv [source file or directory] [target file]

When the second parameter type is a file, the mv command completes file renaming. It renames the given source file or directory to the given target file name.
When the second parameter is the name of an existing directory, there can be multiple source files or directory parameters, and the mv command will move all the source files specified by each parameter to the target directory.When moving files across file systems, mv first copies and then deletes the original file, and the link to the file will also be lost.

# 将webdata 移动到/bin/usr/中
mv  webdata  /bin/usr/

# 将 /usr/lib/下所有的东西移到/zone/中。
mv    /usr/lib/*    /zone


# 是将lib下以txt结尾的所有文件移到/zone中。
mv    /usr/lib/*.txt    /zone

# 将文件temp.txt 修改名字为tempTest.txt
mv   temp.txt  tempTest.txt

[options]Main parameters (several important parameters)
-i: Interactive operation.If the mv operation will cause overwriting of an existing target file, the system will ask whether to rewrite and require the user to answer "y" or "n" to avoid accidentally overwriting the file.
-f : Interactive operations are prohibited.The mv operation does not give any instructions when overwriting an existing target file. After specifying this parameter, the i parameter will no longer have any effect. - r Instructs mv to recursively move all directories and subdirectories listed in the parameter.

1.3.8 ln

• Link command, generate link file link

1.3.8.1 Hard link characteristics

• Having the same i-node and storage block can be regarded as the same file
• Can be accessed through i-node
• Cannot cross partitions
• Cannot be used against directories
• Generally not used

1.3.8.2 Soft link characteristics

• ln -s [source file] [destination file]
  • -s creates soft link
• Similar to Windows shortcuts
• Soft links have their own i-nodes and Blocks, but only the file name and i-node number of the source file are stored in the data block, and there is no actual file data.
• lrwxrwxrwx l soft link The file permissions of soft links are all 777
• Modify any file and the other will change
• Delete the source file and the soft link cannot be used
• The soft link source file must have an absolute path

1.4 File search command

1.4.1 locate

• Searching by file name in the background database is faster
• The data is stored in the /var/lib/mlocate backend database and is updated once a day.
• You can update the database immediately with the updatedb command
• Only file names can be searched
• /etc/updatedb.conf Indexing configuration file
  • PRUNE_BIND_MOUNTS = "yes" All take effect, enable search restrictions
  • PRUNEFS does not search file systems
  • PRUNENAMES ignored file types
  • PRUNEPATHS ignored paths /tmp

1.4.2 whereis

• Search the path where the command is located and where the help documentation is located
• whereis command name whereis ls
  • -b Find only executable files
  • -m only searches help files

1.4.3 which

You can see the alias which ls All you can see are externally installed commands. Unable to view the commands that come with the Shell, such as which cd

1.4.4 Environment variables

/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin

• Defines the path of the system search command
• echo $PATH

1.4.5 find

• file search command
• find [search scope] [search criteria]

1.4.5.1 Search by name

• Avoid large-scale searches, which will consume a lot of system resources

find / -name aaa.log

1.4.5.2 Wildcard characters

• find searches for file names that meet the conditions in the system. If a match is required, use wildcard matching. The wildcard character is an exact match.
• wildcard
  • * matches anything
  • ? matches any character
  • [] matches any character within brackets

find . -name "ab[cdef]"

1.4.5.3 -i

Not case sensitive

find / -iname A.log

1.4.5.4 -user

Search by owner

find /root -user root
find /root -nouser

1.4.5.5 Search by time

find /nginx/access.log -mtime +5

Parameters	Meaning
atime	file access time
ctime	Change file attributes
mtime	Modify file content

Parameters	Meaning
-5	Files modified within 5 days
5	Files currently modified 5 days ago
+5	File modified 5 days ago

1.4.5.6 Search by size

• k lowercase, M uppercase

find . -size 100k

Parameters	Meaning
-8k	Less than 8K
8k	equal to 8K
+8k	Greater than 8K
+8M	Less than 8M

1.4.5.7 Search by i node

find . -inum 123456

1.4.5.8 Comprehensive application

find /tmp -size +10k -a -size -20k

• Find files in the /etc directory that are greater than 10KB and less than 20KB
• -a and Logical AND, both conditions are met
• -o or Logical OR, only one of the two conditions is met

find /tmp -size +10k -a -size -20k -exec ls -lh {} \;

• exec operates on the results of the previous command

1.4.5.9 grep

• Match matching strings in files
• grep "10" access.log
  • -i ignore case
  • -v excludes the specified string
• The find command searches for file names that meet the conditions in the system. If a match is required, use wildcard matching. The wildcard character is an exact match.
• The grep command searches for strings that meet the conditions in the file. If a match is required, use a regular expression to match. The regular expression includes matching.

1.5 Help commands

1.5.1 Basic usage

• man command Get help for a specified command
• man ls View help for ls

1.5.2 Man level

• 1 View the help of the command
• 2 View help for functions that can be called by the kernel
• 3 View help for functions and function libraries
• 4 View help for a special file
• 5 View help for configuration files
• 6 View the game’s help
• 7 View other help
• 8 View help for commands available to your system administrator
• 9 View help for kernel-related files

1.5.3 View command level

• View command level
• 1p: POSIX utilities
• POSIX stands for Portable Operating System Interface of UNIX (abbreviated as POSIX). The POSIX standard defines the interface standards that the operating system should provide for applications.

man -f ls
whatis ls
man 1 ls
man 1p ls

1.5.4 Keyword search

- man -k passwd

1.5.5 Shell internal help

• If whereis is found, it is external; if not found, it is internal.

help cd

1.6 Compression and decompression commands

Suffix .zip .gz .bz2 .tar.gz .tar.bz2

1.6.1 zip format

• Compressed file zip compressed file name source file
• Compressed directory zip -r compressed file name source directory
• Unzip unzip compressed file name

mkdir book
touch book/1.txt
touch book/2.txt
zip -r book.zip book
unzip book.zip

1.6.2 gzip

Command	Example	Meaning
gzip source file	gzip a.txt	Compressed into a .gz format compressed file, the source file will disappear
gzip c source file > compressed file	gzip -c yum.txt > yum.txt.gz	Compressed into a compressed file in .gz format, the source file will not disappear
gzip -r directory	gzip -r xx	Compress all subfiles in the directory, but do not compress the directory
gzip -d compressed file name	gzip -d yum.txt.gz	Decompress the file without retaining the compressed package
gunzip compressed file	gunzip yum.txt.gz	decompress the file without retaining the compressed package

• Compression is to compress files in a directory

1.6.3 .bz2 format compression

| Command | Example | Meaning | | -- | -- | -- | -- | | bzip2 source file | bzip2 1.txt | Compressed to a file in .bz2 format, without retaining the source file | | bzip2 -k source file | zip2 -k 1.txt | Compress to .bz2 format file, retain the source file | | bzip2 -d compressed file name | bzip2 -d 1.txt.bz2 | Decompress the compressed package | | bunzip2 compressed file name | bunzip2 1.txt.bz2 | Unzip the compressed package |

• bzip2 cannot compress directories

1.6.4 tar

• Packaging command
• tar -cvf package file name source file
  • -c package
  • -v show process
  • -f specifies the packaged file name

tar -cvf book.tar book
gzip book.tar
bzip2 book.tar

• x unpack

tar -xvf book.tar

1.6.5 tar.gz compression format

• It can be packaged into .tar format first, and then compressed into .gz format. -z compresses into .tar.gz format. -x decompresses into .tar.gz format.

| Command | Example | Meaning | | -- | -- | -- | -- | | tar -zcvf compressed package name .tar.gz source file | tar -zcvf book.gar.gz book | can be packaged into .tar format first and then compressed into .gz format | | tar -zxvf compressed package name .tar.gz | tar -zxvf book.tar.gz | Decompress tar.gz compressed package | | tar -jcvf compressed package name .tar.bz2 source file | tar -zcvf .tar.bz2 book | can be packaged into .tar format first and then compressed into .bz2 format | | tar -jxvf compressed package name .tar.bz2 | tar -zxvf book.tar.bz2 | Decompress tar.bz2 compressed package |

1.7 Shutdown and restart commands

1.7.1 shutdown

shutdown shutdown command

• -c cancels the previous shutdown command
• -h shutdown
• -r restart

shutdown -r 06:00
shutdown -c

1.7.2 init

Shut down

init 0

Restart

init 6

system runlevel

• 0 shutdown
• 1 but user
• 2 Not fully multi-user, does not include NFS services
• 3 fully multi-user
• 4 not allocated
• 5 Graphical interface
• 6 Restart

1.7.3 logout

Log out

logout

1.8 Mount

1.8.1 Mount command

• mount View the devices mounted on the system

mount 
mount -a

1.8.2 Mount command format

• mount [-t file system] [-o special option] device file name mount point
• Options
  • -t file system ext4 iso9660
  • -o special options

1.8.3 Mount the optical drive

mkdir /mnt/cd
mount -t iso9660 /dev/sr0 /mnt/cdrom

1.8.4 Uninstall the optical drive

umount /dev/sr0
umount /mnt/cdrom

1.8.4 Mount U disk

fdisk -l
mount -t vfat /dev/sdb1 /mnt/usb

• Linux does not support NTFS format by default

1.9 View logged in user information

1.9.1 w

View logged in user information

• USER Login username
• TTY login terminal tty1 local terminal pts/0 remote terminal
• FROM Login IP
• LOGIN login time
• IDLE user idle time
• JCPU The time occupied by all processes in this terminal
• PCPU Time occupied by the current process
• WHAT command being executed

1.9.2 who

View logged in user information

• USER Login username
• TTY login terminal tty1 local terminal pts/0 remote terminal
• LOGIN login time (login IP)

1.9.3 last

View current login and past login user information. Read /var/log/wtmp file by default.

• Username
• Log in to the terminal
• Login IP
• Login time
• Exit time (online time)

1.9.4 lastlog

View the last login time of all users

• Username
• Log in to the terminal
• Login IP
• Last login time

2. shell

• The shell is a command line interpreter that provides users with an interface to send requests to the Linux kernel in order to run programs system-level programs
• Users can use Shell to start, suspend, stop or write some programs
• Shell is also a very powerful programming language, easy to write, easy to debug, and highly flexible.
• Shell is a scripting language for interpretation and execution. Linux system commands can be directly called in Shell.

2.1 View supported shells

• /etc/shells

2.2 echo

• Output command
• --e supports backslash-controlled character conversion

| Control characters | Function | | -- | -- | -- | | \a | Output warning sound | | \b | Backspace key, also known as the left delete key | | \n | newline character | | \r | Enter key | | \t | Tab character, also known as Tab key | | \v | vertical tab character | | \onnn | Output characters according to the octal ASCII code table, where 0 is the number zero and nnn is a three-digit octal number | | \xhh | Output characters according to the hexadecimal ASCII code table, where hh is a two-digit hexadecimal number |

• 30m-47m
• echo -e "\e[1;31m warning \e[0m"

symbol	color
#30m	Black
#31	Red
#32	Green
#33	Yellow
##34	Blue
##35	Magenta
##36	Green
##37	White

2.3 Writing an execution shell

#!/bin/bash
echo -e "\e[1;34m hello world \e[0m"

Grant execution permissions and run directly

chmod 755 hello.sh
./hello.sh

Execute script via Bash call

bash hello.sh

2.4 Aliases

• Command alias == nickname
• Temporarily effective
• alias
• alias rm="rm -i"
• Write environment variable configuration file vi ~/.bashrc
• source ~/.bashrc
• unalias alias delete alias

2.5 Order of effectiveness of commands

• absolute path or relative path
• Alias
• bash internal commands
• The first command found in the directory search order defined by the $PATH environment variable

2.6 Command shortcut keys

Command	Meaning
ctrl+c	Forcefully terminate the current command
ctrl+l	clear screen
ctrl+a	Move the cursor to the beginning of the command line
ctrl+e	Move the cursor to the end of the command line
ctrl+u	Delete from the cursor position to the beginning of the line
ctrl+z	Put the command into the background
ctrl+r	Search in command history

2.7 Historical commands

• history [options] [history command save file]
• Options
  • -c Clear command history
  • -w writes the history commands in the cache to the history command save file ~/.bash_history
• 1000 entries are saved by default /etc/profile HISSIZE=10000

2.8 Call

• Use the up and down arrows to recall previous history commands
• Use !n to repeatedly execute the nth historical command
• Use !! to repeat the previous command
• Use the ! character to repeat the last command starting with this string

2.9 Output redirection

2.9.1 Standard input and output

device	device file name	file descriptor	type
keyboard	/dev/stdin	0	standard input
monitor	/dev/stdout	1	standard output
Monitor	/dev/stderr	2	Standard Error Output

Type	Symbol	Function
Standard output redirection	Command > File	Output the correct output of the command to the specified file or device in an overwriting manner
Standard output redirection	Command >> File	Output the correct output of the command to the specified file or device in append mode
Error output redirection	Command>File	Output the error output of the command to the specified file or device in an overwriting manner
Error output redirection	Command>>File	Output the error output of the command to the specified file or device in append mode
Save the correct output and error output at the same time	Command>File 2>&1	Save both the correct output and the error output to the same file in an overwriting manner
Save the correct output and error output at the same time	Command>File 2>>&1	Save both the correct output and the error output to the same file by appending
Save the correct output and error output at the same time	Command &> File	Save the correct output and error output to the same file in an overwriting manner
Save the correct output and error output at the same time	Command &>> File	Save the correct output and error output to the same file by appending
Save the correct output and error output at the same time	Command>>File 1 2>File 2	Append the correct output to File 1 and append the error output to File 2 in an overwriting manner

2.9.2 Input redirection

• command <file takes a file as input to the command

• Command << identifier identifier uses the content between identifiers as input to the command

• wc < access.log

• wc <>

2.10 Pipe symbols

2.10.1 Sequential execution of multiple commands

Multiple command executors	Format	Function
;	Command 1;Command 2	Multiple commands are executed without any logical connection between the commands
&&	Command 1&& Command 2	Logical AND When command 1 is executed correctly, command 2 will be executed. When command 1 is executed incorrectly, command 2 will not be executed
`		`

• date;ls;date;ls
• ls && echo yes || echo no

2.10.2 Pipe symbol

• The correct output of command 1 will be used as the operation object of command 2
• Command 1|Command 2

ls /etc/ | more
netstat -an | grep ESTABLISHED | wc -l

2.10.3 Wildcards

Match filenames and directory names

Wildcard	Function
?	matches any character
*	matches 0 or any characters, that is, it can match any content
[]	matches any character in the square brackets
[-]	matches any character in the square brackets, - represents the range
[^]	matches a character that is not enclosed in square brackets

2.10.4 Other symbols

Symbol	Function
''	single quote.All special symbols within single quotes, such as $ and ` have no special meaning
""	Double quotation marks. Special symbols in double quotation marks have no special meaning, except $ ` , which has the meaning of calling variable values, quoting commands and escaping
``	Backticks, expanded are system commands
$()	Same as backtick
#	In shell scripts, lines starting with # represent comments
$	The value used to call the variable
\	escape symbol

 a=`ls`
 b=$(ls)

3. vi editor

• VI visual interface
• Visual interface
• Similar to notepad in windows
• vim supports multi-level undo
• Cross-platform
• syntax highlighting
• Support graphical interface

3.1 Operating modes

Schema name	Meaning
Command Mode command mode	mode waiting for input
Insert Mode input mode	Edit mode, used to enter text
Last Line Mode bottom line mode (last line, last line)	You can enter commands, search, and save

• vim + abc
• vim +3 abc
• vim +5 abc
• vim +/xxx abc
• vim a b c :n

3.2 Common commands

3.2.1 Bottom row mode

• :w save
• :q exit
• :! Force save
• :ls lists all files
• :n next
• :N Previous
• :15 Jump to the specified line
• /xxx searches the xxx string backward starting from the cursor position
• ?xxx Search forward starting from the cursor position

3.2.2 Command mode

• h Move cursor left

• j Move cursor down

• k Cursor moves up

• l Move cursor right

• ctrl+f page down (front)

• ctrl+b page up

• ctrl+d to turn down half a page

• ctrl+u turn up half a page

• dd deletes the line under the cursor

• o Insert a line below the line where the cursor is and switch to input mode

• yy copies the line where the cursor is located

• p Paste below the line where the cursor is

• P Paste above the line where the cursor is

4. Users and user groups

• Everyone who uses the operating system is a user
• A user group is a group of users with the same system permissions

4.1 User groups

4.1.1 /etc/group

• /etc/group stores all user group information in the current system
• group:x:123:abc,def
• Group name: Group password placeholder: Group number: List of user names in the group
• The root group number is 0
• 1-499 System-reserved numbers reserved for installed software and services
• User groups manually created by users start at 500
• The group password placeholders are all x

4.1.2 /etc/gshadow

• Store the password information of the user group in the current system
• One-to-one correspondence with the records in the group
• Group: * : :abc
• Group name Group password Group manager User name in the group

4.1.3 /etc/passwd

• Store information about all users in the current system
• user:x:123:456:xxxxx:/home/user:/bin/bash
• Username: Password placeholder: User number: User comment information: User home directory: Shell type

4.1.4 /etc/shadow

• Store the password information of all users in the current system
• user:xxx:::::::
• Username: Password:

4.2 User operations

Add group

groupadd student

Modify group name

groupmod -n stu student

Modify group number

groupmod -g 111 stu

Add group and specify number

groupadd -g 222 teacher

Delete group

groupdel 222

Add group

groupadd teacher

Assign a group to the user

useradd -g teacher zhangsan

Assign a group to the user

useradd -g teacher lisi

Specify working directory for user

useradd -d /home/zhangsan zhangsan

Specify comments

usermod -c iamateacher zhangsan

Modify username

usermod -l zhangsan zhangsan2

Specify folder

usermod -d /home/zhangsan2 zhangsan2

Modify the group to which the user belongs

usermod -g stu zhangsan2

Delete user

userdel zhangsan2

Delete the folder it belongs to

userdel -r lisi

5. user command

Show logged in user name

whoami

Display the specified user information, including user number, user name, main group number and name, and subsidiary group list

id zhangsan

Display all groups to which user zhangsan belongs

groups zhangsan

Show user details

finger zhangsan

6. Appendix

6.1 System startup

6.1.1 BIOS

• After the computer is powered on, the first thing is to read the boot program flashed into the ROM chip. This program is called (Basic Input/Output System)

6.1.2 Hardware self-test

• The BIOS program first checks whether the computer hardware can meet the basic conditions for operation. This is called "Hardware Self-Test" (Power-On Self-Test)
• If there is a problem with the hardware, the motherboard will beep with different meanings and the startup will be aborted.If there is no problem, the screen will display CPU, memory, hard disk and other information.

6.1.3 Startup sequence

• After the hardware self-test is completed, the BIOS transfers control to the next stage of the startup program.
• At this time, the BIOS needs to know which device the "next stage startup program" is stored in.
• The BIOS needs to have a ranking of external storage devices, and the device ranked first is the device that gives priority to transfer control.This sorting is called "Boot Sequence"
• The BIOS follows the "boot order" and transfers control to the storage device ranked first.
• At this time, the computer reads the first sector of the device, which is the first 512 bytes.If the last two bytes of these 512 bytes are 0x55 and 0xAA, it indicates that the device can be used for booting; if not, it indicates that the device cannot be used for booting, and control is transferred to the next device in the "boot sequence".
• The first 512 bytes are called the "Master boot record" (MBR)

6.1.4 Structure of Master Boot Record

• The "Master Boot Record" is only 512 bytes, so it can't hold much.Its main function is to tell the computer where to find the operating system on the hard disk.
  • (1) Bytes 1-446: are used to record the startup information of the system and call the machine code of the operating system
  • (2) Bytes 447-510 (64 bytes): Partition table. The function of the partition table is to divide the hard disk into several areas.
  • (3) Bytes 511-512: Master boot record signature (0x55 and 0xAA)

6.1.5 Partition table

• Disk partitioning is dividing the disk into several logical parts using a partition editor
• Once the disk is divided into multiple partitions, different types of directories and files can be stored in different partitions.
• The "Master Boot Record" therefore must know which partition to transfer control to
• The length of the partition table is only 64 bytes, which is divided into four items, each item is 16 bytes.Therefore, a hard disk can only be divided into four first-level partitions, also called "primary partitions"
  • (1) The 1st byte: If it is 0x80, it means that the primary partition is the active partition, and control is transferred to this partition.Only one of the four primary partitions can be activated.
  • (2) Bytes 2-4: The physical location of the first sector of the primary partition (cylinder, head, sector number, etc.).
  • (3) The 5th byte: Primary partition type, such as FAT32, NTFS, etc.
  • (4) Bytes 6-8: The physical location of the last sector of the primary partition.
  • (5) Bytes 9-12: The logical address of the first sector of the primary partition.
  • (6) Bytes 13-16: The total number of sectors in the primary partition.

6.1.6 Hard disk boot

• The control of the computer will be transferred to a certain partition of the hard disk.
• Of the four primary partitions, only one is active.The computer will read the first sector of the activated partition, which is called the "Volume boot record" (VBR).

6.1.7 Operating system

• After control is transferred to the operating system, the operating system's kernel is first loaded into memory.
• Taking the Linux system as an example, first load the kernel under the /boot directory.After the kernel is loaded successfully, the first program to run is /sbin/init.It generates an init process based on the configuration file (/etc/initab for Debian systems).This is the first process after Linux starts. The pid process number is 1, and other processes are its descendants.
• Then, the init thread loads various modules of the system, such as window programs and network programs, until the /bin/login program is executed, the login interface jumps out, and the user enters the user name and password.

7 Process Management

7.1 Process

• A process is a program or command being executed. Each process is a running entity, has its own address space and uses certain system resources.
• A process is a program that is being executed

7.2 Introduction to process management

• Determine the status of the server
• View all processes in the system
• Kill the process. Kill the process only if it cannot be closed.

7.3 Process view command (ps)

• ps aux View all processes in the system, using BSD operating system format
• ps -le View all processes in the system, using Linux standard format
• TTY is an abbreviation for TeleType, which originally refers to a teletype machine, which is a device that reads and sends information through a serial line using a printer keyboard.
• pts(pseudo['su:doʊ]-terminal slave) is the so-called pseudo terminal or virtual terminal

7.3.1 Options

Parameters	Meaning
-a	Display all processes in a terminal
-u	Display the owned user and memory usage of the process
-x	Show processes without a controlling terminal
-l	Long format display, display more detailed information

7.3.2 Result field meaning

Data	Meaning
USER	Which user created this process
PID	ID number of the process
%CPU	The percentage of CPU resources occupied by this process. The higher the occupancy, the more system resources are consumed
%MEM	The percentage of physical memory occupied by this process. The higher the occupancy, the more system resources are consumed
VSZ	The percentage of virtual memory occupied by this process, in KB
RSS	The actual physical memory size occupied by this process, in KB
TTY	In which terminal this process is running.tty1~tty7 represent local control terminals, tty1~tty6 are character terminals, and tty7 is a graphical terminal.pts/0~255 represents a virtual terminal, ? indicates that this terminal is started by the system
STAT	Process status
START	The start time of the process
TIME	This process takes up computing time of the CPU. The higher the value, the more system resources are consumed
COMMAND	The command name that spawned this process

7.3.3 Process status (STAT)

Parameter	Meaning
R(Runing)	Running
S(Sleep)	Sleep
T(Terminated)	Stop
S(Son)	Contains child processes
+	in the background

7.4 pstree

• pstree [选项]
  • -p displays process PID
  • -u displays the user who owns the process

7.5 Viewing processes (top)

• top

top -b -n 1 > top.txt

7.5.1 Options

Options	Meaning
-b	Use batch mode output, generally used in conjunction with -n
-n	times, specify the number of times the top command is executed.Generally used with the -b option
-d	Number of seconds, specifies how many seconds the top command is updated every few seconds.Default is 3 seconds

7.5.2 Interactive mode commands

Options	Meaning
? or h	Display help in interactive mode
P	Sort by CPU usage, the default is this option
M	Sort by memory usage
N	Sort by PID
q	exit top

7.5.3 Status bar

7.5.3.1 The first line contains task queue information

Content	Description
12:12:12	Current time of the system
up 1 day 5:33	System running time, this machine has been running for 1 day, 5 hours and 33 minutes
2 users	Two clients are currently logged in
load average 0 0 0	The average load of the system in the previous 1 minute, 5 minutes, and 15 minutes.It is generally believed that the load is smaller if it is less than 1 hour, and the load is greater than 1 hour

7.5.3.2 The second line of process information

Content	Description
Tasks: 100 total	Total number of processes in the system
1 running	Number of running processes
94 sleeping	The process of sleeping
0 stopped	Process being stopped
0 zombie	Zombie process.If it is not 0, check it

7.5.3.3 The third line is CPU information

Content	Description
Cpu(s): 0.1%us	Percentage of CPU occupied by user mode
0.1%sy	Percentage of CPU occupied by system mode
0.0%ni	Percentage of CPU occupied by user processes that have changed their priority
99.7%id	CPU percentage of idle CPU
0.1%wa	Percentage of CPU occupied by processes waiting for input/output
0.1%hi	Percentage of CPU occupied by hard interrupt request service
0.1%si	Percentage of CPU occupied by soft interrupt request service
0.0%st	st (Steal time) virtual time percentage, that is, when there is

7.5.3.4 The fourth line is physical memory information

Content	Description
Mem: 1030720k total	Physical memory problem, unit is KB
551860k used	Amount of physical memory used
478860k free	The amount of free physical memory, the virtual machine is allocated 1024M memory, 538M is used, and 467M is free
43180k buffers	As the amount of buffer memory, it can store the data that needs to be written to the hard disk to speed up the writing of data

7.5.3.5 The fourth line exchanges partition information

Content	Description
Swap: 2047992k total	Total swap partition (virtual memory) size
536k used	The size of the swap partition that has been used
2047456k free	Free swap partition size
368164k cached	Read data that needs to be read frequently from the hard disk into the memory, speeding up the reading of data

7.6 Kill the process (kill)

7.6.1 Process signals

• kill -l to view available process signals |Signal |Code |Signal name |Description |Example| | -- | -- | -- | -- | -- | |1 |SIGHUP |This signal causes the process to shut down immediately, then rewrite and read the configuration file before restarting, and restart smoothly |kill -1 -HUP process number| |2 |SIGINT |Program termination signal, used to close the foreground process, equivalent to ctrl+c | |9 |SIGKILL |Used to end the running of the program immediately. This signal cannot be blocked, processed or ignored. It is generally used to force a stop | |15 |SIGTERM |A signal to terminate the process normally, the default signal of the kill command.If it cannot be terminated normally, the SIGKILL signal will be tried |

7.6.2 Kill the process

sleep.sh

#!/bin/bash
i=0
while [ $i -le 1000 ]
 do
   echo $(date)
   sleep 1s
 done

sh sleep.sh &
ps -ef | grep sleep.sh

kill  进程号

8. System resource view

8.1 vmstat

• Monitor system resource usage status
• vmstat [刷新延时 刷新次数]

vmstat 1 3
procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu-----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
 1  0    532 329932  99388 459768    0    0    16    81   59   50  3  1 96  0  0

8.1.1 (procs) process information field

Classification	Parameters	Meaning
procs	r	The number of processes waiting to run. The larger the number, the busier the system
procs	b	The number of processes that cannot be awakened. The larger the number, the busier the system

8.1.2 memory (memory information field)

Classification	Parameters	Meaning
memory	swpd	The size of the Swap space used, in KB
memory	free	Free memory capacity, unit KB
memory	buff	buffer memory capacity, unit KB
memory	cache	Cache memory capacity, unit KB

8.1.3 swap (swap partition information)

• If the larger the number of si and so, it means that data often needs to be exchanged between disk and memory, and the system performance will be worse.

Classification	Parameters	Meaning
swap	si(in)	The amount of data swapped from disk to memory, in KB
swap	so(out)	The amount of data swapped from memory to hard disk, in KB

8.1.4 io (disk reading and writing)

• The larger the bi and bo numbers are, the busier the disk I/O is.

Classification	Parameters	Meaning
io	bi(in)	Problem reading data from block device, unit is block
io	bo(out)	The total amount of data written to the block device, in blocks

8.1.5 system (system information field)

• The larger the in and cs numbers are, the busier the communication between the system and the interface device is.

Classification	Parameters	Meaning
system	in(interrupt)	Number of interrupted processes per second
system	cs(switch)	Number of event switches per second

8.1.6 CPU (CPU information field)

Classification	Parameters	Meaning
CPU	us(user)	Percentage of CPU computing time consumed by non-kernel processes
CPU	sy(system)	The percentage of CPU computing time consumed by the kernel process
CPU	id(idea)	Percentage of idle CPU
CPU	wa(wait)	Percentage of CPU consumed waiting for I/O
CPU	st(steal)	Percentage of CPU stolen by the virtual machine

8.3 free

• View memory usage status
• free [-b|-k|-m|-g]
• Options
  • -b in bytes
  • -k in KB bytes
  • -m in MB bytes
  • -g in GB bytes

# free -m
             total       used       free     shared    buffers     cached
Mem:          1006        687        319          0         98        449
-/+ buffers/cache:        139        866
Swap:         1999          0       1999

8.3.1 First line

Parameters	Meaning
total	Total memory
used	The amount of memory that has been used
free	Number of free memory
shared	Amount of memory shared by multiple processes
buffers	Number of buffer memory
cached	Number of cached memories

8.3.2 Second line

Parameters	Algorithm	Meaning
- buffers/cache	used-buffers-cached in the first line	The amount of memory that has been used minus cache and buffering
+ buffers/cache	free+buffers+cached in the first line	The amount of free memory plus cache and buffer memory

8.3.3 The third line

Parameters	Meaning
total	The total number of swaps, the default unit is K
used	The number of swaps that have been used, the default unit is K
free	The number of free swaps, the default unit is K

8.6 View kernel related information

• uname

# uname -a
Linux localhost 2.6.32-279.el6.i686 #1 SMP Fri Jun 22 10:59:55 UTC 2012 i686 i686 i386 GNU/Linux
# uname -s
Linux
# uname -r
8.6.32-279.el6.i686

8.7 Check the operating system bit number

file /bin/ls

8.8 View release version

lsb_release -a

8.9 View release version

yum install redhat-lsb -y
lsb_release -v

9. System scheduled tasks

• Some tasks, such as backing up databases, need to be performed when the system is idle.

9.2 crontab

• Scheduled tasks can be executed cyclically and regularly
• cron

systemctl restart crond.service

9.2.3 crontab settings

• crontab [options]
• Options
  • -e edit crontab scheduled tasks
  • -l Query crontab tasks
  • -r deletes all crontab tasks for the current user

* * * * *  执行的任务

9.2.3.1 Syntax

# .---------------- minute (0 - 59)
# |  .------------- hour (0 - 23)
# |  |  .---------- day of month (1 - 31)
# |  |  |  .------- month (1 - 12) OR jan,feb,mar,apr ...
# |  |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
# |  |  |  |  |
# *  *  *  *  * user-name command to be executed

9.2.3.2 Location

Project	Meaning	Scope
1st star	Minutes in 1 hour	0~59
2nd star	Hour of the day	0~23
3rd star	Day of the month	1~31
4th star	Which month of the year	1~12
5th star	Day of the week	0~6

9.2.3.3 Special symbols

Symbol	Meaning	Example
*	represents any time	For example, the first star represents execution every minute of an hour
,	Represents discontinuous time	For example, "1,2,3" means executing commands at 1, 2, and 3 minutes per hour
-	represents a continuous time range	For example, "1-5 * **", represents the execution of the command from the 1st to the 5th minute of every hour
*/n	Represents how often to execute the command	For example, "/10" means to execute the command every 10 minutes
0 0 1,10 * 1	Executed on the 1st and 10th of each month, at 0:00 every week

9.2.3.4 Case

Symbol	Meaning
10 22 *	Executed at 22:10 every day
0 15 1	Executed every week at 15:00
0 5 5,10	Executed at 5 a.m. on the 5th and 10th of each month
10 5 1-5	Execute the command at 5:10 am every Monday to Friday
/10 10	Executed every 10 minutes at 10 a.m. every day

9.2.3.5 Precautions

• All options cannot be empty and must be filled in
• The minimum unit of crontab is minutes and the maximum unit is days.
• Regardless of whether you write commands or scripts, use absolute paths.

9.3 System scheduled tasks

crontab -e is a command executed by the user. Different user identities can execute their own scheduled tasks. If you need the system to perform scheduled tasks, you can edit the /etc/crontab file /etc/crontab can specify the shell, path, email sending and home directory

9.3.1 /etc/crontab

• Modify the /etc/crontab configuration file

5 5 * * * echo `date` >> /root/date.log

10. Actual combat tasks

10.1 Monitor nginx

nginx.sh

#!/bin/bash
local nginx
nginx=`ps -ef |grep nginx|grep -v grep|wc -l`
 if [ $nginx -gt 2 ];then
    echo "your nginx is running"
    exit 0
 else
    /bin/systemctl start nginx.service
    exit 1
fi

10.2 Monitor mysql status

mysql.sh

#!/bin/sh
PortNum=`netstat -lnt|grep 3306|wc -l`
if [ $PortNum -eq 1 ]
then
 echo "mysqld is running."
else
 echo "mysqld is stoped."
fi

10.3 mysql backup script #

mysql_backup.sh

#!/bin/bash
DATE=$(date +%F_%H-%M-%S)
HOST=127.0.0.1
DB=test
USER=root
PASS=abcd1#EFG
MAIL="xxxx@qq.com"
BACKUP_DIR=/data/db_backup
if [ ! -d "$BACKUP_DIR" ];then
 mkdir -p $BACKUP_DIR
fi
SQL_FILE=${DB}_FULL_$DATE.sql
BAK_FILE=${DB}_FULL_$DATE.zip
cd $BACKUP_DIR
if mysqldump -h$HOST -u$USER -p$PASS -B $DB > $SQL_FILE; then
  zip $BAK_FILE $SQL_FILE && rm -rf $SQL_FILE
  if [ ! -s $BAK_FILE ]; then
    echo "$DATE 备份失败" | mail -s "备份失败" $MAIL
  fi
else
  echo "$DATE 备份失败" | mail -s "备份失败" $MAIL
fi
find $BACKUP_DIR -name '*.zip' -ctime +14 -exec rm {} \;

Login authorization

After authorization, you don’t need to enter your password the next time you log in.

ssh-copy-id 47.104.220.xx

If /root/.ssh/id_rsa is not generated, you can generate the key through the following command

ssh-keygen -t rsa

Turn off firewall

close iptables #

The iptables command is a commonly used firewall software on Linux

Function	Command
Stop firewall	systemctl stop firewalld.service
Permanently turn off the firewall	systemctl disable firewalld.service

Confirm to disable selinux

Security-Enhanced Linux (Security-Enhanced Linux), referred to as SELinux, is a Linux kernel module and a security subsystem of Linux. The main function of SELinux is to minimize the resources accessible to the service process in the system (the principle of least privilege).

Function	Command
Check status	getenforce
Check status	/usr/sbin/sestatus -v
Temporary shutdown	setenforce 0
permanently closed	/etc/selinux/config SELINUX=enforcing改为SELINUX=disabled

Install dependent modules

yum  -y install gcc gcc-c++ autoconf pcre pcre-devel make automake
yum  -y install wget httpd-tools vim